A capacitance electronic disc system has been described by Clemens in U.S. Pat. No. 3,842,194. The system as described comprises a molded plastic disc having audio, video and color information in the form of geometric variations in a spiral groove in the disc surface. These discs are coated first with a conductive material, such as a metal layer, which acts as a first electrode, and then with a dielectric layer, such as an inert polymer layer. A metal tippped stylus acts as a second electrode of a capacitor, and the information signals are mointored by the stylus which notes changes in capacitance between the stylus and the disc surface as the information, in the form of depressions, passes beneath the stylus when relative motion is established between the disc and the stylus.
Further developments and improvements in the system have produced a video disc which is made of a conductive plastic material, e.g., a vinyl chloride polymer resin containing sufficient amounts of conductive particles, such as conductive carbon particles, so that the disc can provide capacitance readout. The carbon particles are surrounded by organic materials, such as the plastic resin and various processing additives, which provide a dielectric surface layer on the conductive particles. This development has eliminated the need for separate coatings of metal and dielectric on the plastic disc. Video discs which do not require a grooved surface have also been developed. The stylus is maintained in synchronization with the information pattern or track by means of electrical signals on either side of the information track, rather than physically by means of the grooved walls.
In order to prevent undue wear between the disc and stylus, a lubricant layer is applied to the disc surface by evaporation. Wang et al., in U.S. Pat. No. 4,275,101, has described the application of certain methyl alkyl siloxane compositions having the general formula: ##STR1## wherein R.sub.1 and R.sub.2 are alkyl groups of 4-20 carbon atoms, x is an integer of 2-4, y is an integer of 0-2, and wherein the sum of x and y is 4 or less, to these discs as an improved class of lubricants for video disc applications, which lubricants have improved stability and resistance.
Keizer, in U.S. Pat. No. 4,162,510, discloses a novel keel tipped pickup stylus structure for use in the capacitance electronic disc information recovery system. The keel tipped pickup stylus comprises a dielectric support element having a body, a constricted terminal portion and shoulders interconnecting the body with the constricted terminal portion. The electrode surface is remote from the prow end of the stylus. The stylus, formerly made of metallized sapphire, has also been improved so that metallized diamond can be employed. Diamond is a harder, longer wearing material than sapphire, and is thus preferred.
The information record or disc, in accordance with a preferred format of this sytem, incorporates the disc surface, which upon playback cooperates with a tracking or pickup stylus electrode to establish information-representative capacitance variations. The tracking stylus and groove shapes are preferably sufficiently correlated so that during playback a surface of the conductive stylus electrode is closely adjacent the dimension-varying bottom of the groove. A desirably linear relationship between the information-representative dimension variations in the groove bottom and the capacitance presented between the stylus electrode and the conductive disc results when relative motion between the stylus and groove occurs. Circuitry responding to such capacitance variations may readily reconstitute the recorded information in an electrical signal form with an acceptable signal-to-noise ratio. While the obtained signal-to-noise ratio of the capacitance variations is acceptable, it would be desirable to obtain an enhanced or improved signal-to-noise ratio from the surface of the conductive disc. Therefore, the search continues for means and methods of improving or increasing the signal-to-noise ratio obtainable from a capacitance electronic disc system including a conductive disc formed from a plastic resin containing dispersed conductive particles.